The present invention relates to apparatus and a method for forming an elongate building panel having a two-dimensional section profile into a curved configuration for use in constructing frameless building structures.
The increased cost of building construction has necessitated the exploration of alternate forms of construction with a view towards minimizing costs. One method of decreasing the costs of construction is to utilize building structures which are less labor intensive to construct. One type of building construction in which labor expenses can be minimized is a frameless building construction comprised of arcuate, generally semicircular panels in which the panels not only provide the weather-proof skin but the structural support for the building as well.
Constructing frameless building structures from arcuate metal panels is well known. However, the size of such buildings is generally quite restricted because of the strength required of the building panels, and particularly their resistance to bending loads on the panels which result from external forces on the structure, such as wind, snow and the like. The weight of the panels themselves, which are typically steel or aluminum, also improve bending loads on the panels.
The panels used to form a frameless, arcuate structure must be bent to their desired arcuate configuration. Bending a completely flat panel causes no difficulties, but a flat panel has little resistance to bending loads, and thus provides insufficient structural strength for all but very small buildings. To enhance the resistance of the panel to bending, it is generally provided with a two-dimensional profile. However, forming such a panel into a curved configuration is quite difficult. Such a panel is generally bent about its outermost surface to form the panel into a curved shape, and the interior portion of the two-dimensional panel section obviously must contract to accommodate the curving of the panel about its outermost surface.
Attempts have been made in the past to curve the building panel by simply passing in between a pair of feed rolls, and bending it by using a curving roll which forces the panel into an arcuate configuration. While acceptable for panels with little depth, this technique has been found to be deficient when panels having substantial depth are used because the side walls of the panel and the internal portion thereof collapse, thus distorting the panel.
To accommodate the collapsing of the internal portion of the panel such internal portions are generally crimped, as illustrated in the patent to Ouellet, U.S. Pat. No. 3,111,788, and the patent to Knudson, U.S. Pat. No. 3,902,288. While such crimping techniques allow the use of a curved panel with a two-dimensional section profile, the crimps themselves significantly weaken the resistance of the interior portion of the panel to tension and compression loads, and thus the resistance of the panel as a whole to bending loads. The weakened resistance of the crimped panel to bending loads substantially defeats the object of using the two-dimensional panel.
As an alternative to the crimping techniques discussed above, the patent to Goodwill et al., U.S. Pat. No. 3,173,225, proposes a panel in which the side walls of the panel are squeezed to extrude the panel into a curved configuration. However, the compressive forces necessary to achieve the intended object of Goodwill are extremely large, and if such large forces were exerted on the panel in the apparatus proposed by Goodwill, it would appear that the panel would simply be squeezed out of the machine. Applicant is unaware of use in the industry of the system proposed by Goodwill.